RTTI inconsistency

[Jim Dehnert]

> From: Nathan Sidwell <sidwell at codesourcery.com>
> 
> Hi,
> there is an inconsistency in the documentation of how a vtable
> points to the type_info object for that type.
> 
> The abi layout document Run-Time Type Information (RTTI) section states,
> 
> 3.Every vtable shall contain one entry pointing to an object derived
> 	from std::type_info. This entry is located at the word preceding
> 	the location pointed to by the vptr (i.e., entry "-1"). The
> 	entry is allocated in all vtables; for classes having virtual bases
> 	but no virtual functions, the entry is zero. This entry is coded
> 	as an offset with respect to the virtual table origin, rather than as
> 	a pointer (thereby avoiding run-time relocations). 

This one is incorrect.  I've fixed it.  Thanks for the observation.

> but the closed issues document section A-6 ends by saying
> 	[991028 all] The current definition, in the ABI data layout document,
> 	has been updated with Daveed's changes, and is accepted. Note that we
> 	are back to using a pointer to RTTI in the vtable (see B-8)...
> 
> Also the Virtual Table Layout section of the ABI document says,
> 	The typeinfo pointer points to the typeinfo object used for RTTI.
> 	All entries in each of the vtables for a given class must point to the
> 	same typeinfo object. A correct implementation of typeinfo equality is
> 	to check pointer equality. 
> 
> so which is it? An offset or a pointer? (I think it has to be a pointer to
> get uniqueness.)

-	    Jim Dehnert		dehnert at sgi.com
				(650)933-4272